Fun and easy science experiments for kids and adults.
Microwave light bulb
Physics
Place a light bulb in the microwave oven and light it using the microwaves! This is an experiment about microwaves, excitation and light bulbs.
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Video
Materials
- 1 microwave oven
- 1 incandescent light bulb
- 1 microwave-safe cup
- Water
Warning!
In this demonstration, metal is placed in the microwave oven. This can possibly damage or shorten the lifespan of the microwave oven.Step 1
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The microwave oven in the video had some kind of sensor that sensed that something was funky, and therefore turned off the microwaves after five seconds. Other microwave ovens I have tested have not had this function, and then you have to turn it off yourself to prevent the light bulb from bursting.
Short explanation
An incandescent light bulb lights up when its filament gets warm enough. In normal cases, this is done by an electric current passing through the filament. Here it's instead done by heating the filament with microwaves.Long explanation
The microwaves pass through the glass of the light bulb and hit the filament. There, the microwaves are absorbed by electrons. These become excited and end up one step further out of the atomic nuclei they orbit. However, this state is unstable and the electrons soon fall back to their ground state. When they fall back, they dispose of the absorbed energy in the form of light. This excitation can be compared to if Earth received a burst of energy that made it jump out to Mars' orbit, and then jump back to its original orbit while emitting a burst of light. When the light bulb shines, an energy transformation takes place; from electromagnetic energy in the microwaves, to short-term stored potential energy in the filament (the excited electrons), and finally to electromagnetic energy in light. This is how a light bulb shines. But normally, it's not microwaves that excite the electrons in the filament, but an electric current that flows through the filament.A cool thing is that the demonstration works even if the filament breaks! The filament doesn't need to be connected to the rest of the light bulb. By placing the metal base in water, you protect it from the full effect of the microwave oven. Because metal is not really suitable to place in a microwave oven. In some cases, it can even be downright dangerous. Metals contain freely moving electrons. When microwaves hit metal, the electrons on the surface of the metal begin to move back and forth very quickly. This acts as a wall for the microwaves and they are reflected instead of absorbed. If there is also pointy metal in the microwave, the electrons can be concentrated in a small area, which results in a large charge difference - voltage - compared to the surroundings. This voltage can lead to a discharge of electrons flowing to or from the surroundings. If the voltage in the metal becomes really high, the air loses its insulating ability and electrons begin to flow straight through the air. Just like lightning in a thunderstorm. If the lightning bolt reaches the walls of the microwave oven, it may burn small holes in it. It can also spread to the electronics in the microwave and destroy it. But even if no flash occurs from pointy metal, reflected microwaves from smooth metal can be absorbed by the microwave oven itself and damage it. In extreme cases it can start to burn. But small amounts of metal pose no major risk. There is some risk of damage to the microwave oven, but no risk of bodily harm.
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